Hey, yea, I met my cousin after we were married as well. We didn't expressed our feelings to each other but I felt really guilty falling for her when I knew we were both married. The feelings were really strong. I read a lot of advises on situations like this... The best thing to do is actually "Let her go."
Because holding on will bring pain and suffering on both parties. You cannot make her separate her husband because of YOU, but because she cannot be with her current husband. It is only then that you guys can be together. Let her make the choice without your influence. This process can take years so don't sit and tap your fingers waiting, lol.
Yea, it was so hard to forget about her for about the first month. I missed her every hour. It has gotten better now though. I still think about her and keep in touch with her but at least I can be normal.